Salestax rates are found on the item list for Desktop, in the Salestax area for QuickBooks Online.
Do not just update your QuickBooks salestax rates in-line.
Add new rates codes, and leave the old ones as is for reporting and auditing purposes.
If we're doing it, we'll rename the old ones first, so the new names will be the same names you're familiar with.
I or one of my bookkeepers can come out and fix this for your business, plus anything else you want help with.